Abstract [en]

In single exposure, divergent beam phototesting, an originally collimated ultraviolet beam is diverged by an optkal lens to give a circular ultraviolet light field with attenuating irradiance towards its periphery. The chromatic aberration, caused by the lens, and its influence on the erythemal effectiveness of the field has been investigated. Spectral measurements (250-400 nm) were performed along the 20 mm radius of the field in steps of 1 mm. The corresponding erythemal effectiveness was calculated after adjustment of the spectral irradiance according to the erythema action spectrum recommended by the Commission Internationale de l' Éclairage (CIE). The erythemal effectiveness of the irradiance field attenuated towards the periphery and stabilized at about 80% of the maximum value at the centre. Knowledge of this is important for dosimetry in skin photobiology and data interpretation. The divergent beam method was used in parallel with the traditional method on three volunteers.

Ilias, Michail A.

Abstract [en]

This thesis concerns the development of quantitative phototesting for the investigation of individual skin sensitivity to ultraviolet (UV) radiation, and the assessment of pigmented skin lesions (PSL) in terms of blood perfusion estimates. In both cases, laser Doppler perfusion imaging (LDPI) was used to quantify the perfusion.

The proposed phototesting method is based on a single exposure to a divergent UVB beam, which produces a continuous, radially attenuating dose field covering an area with a diameter of 4.5 cm. In order to meet the demands posed by this approach, two-dimensional dosimetry was developed, the entire dose field was adapted to the standard erythemal action spectrum for humans, and a spatially resolving technique (LDPI) was used for objective quantification of the skin response. Data analysis methods were developed, enabling the determination of minimal erythemal dose (MED) and the extraction of dose-response information. The method was evaluated on a normal material (20 subjects), proving a good reproducibility of the MED and enhanced possibilities to extract individual dose-response information. In the study of anti-inflammatory effects (16 subjects) of topically applied substances, linear curve-fitting (0.89 ≤ R2 ≤ 0.98) was shown to adequately describe the relationship between dose and response in the dose range immediately above the MED. The gradient of the derived post MED-lines was used as a measure of the response aggressiveness. The results are promising and warrant further evaluation, e.g. in the investigation of patients with suspected photodermatoses.

This thesis also presents a method for the extraction and presentation of blood perfusion data of pigmented skin lesions in conjunction with optical information on the lesions' spatial extent. The boundaries of pigmented lesions could successfully be delineated, using standard image processing steps, in the total light intensity images given by LDPI. Classical blood perfusion measures such as mean perfusion and perfusion quotients was confined to the ROI, making relevant comparison to corresponding values of neighbouring healthy tissue possible. This data analysis approach was used on a pooled group of PSL showing promising results. The method may prove to be a useful adjunct in the discriminative assessment of pigmented skin lesions.